Identification of angiotensin I-converting enzyme inhibitory peptides from koumiss, a traditional fermented mare's milk

Angiotensin I-converting enzyme (ACE) inhibitory activities in untreated koumiss and koumiss digested with ACE, pepsin, trypsinase, and chymotrypsin were compared and analyzed. Four novel ACE inhibitory peptides (P-I, P-K, P-M, and P-P) were purified using ultrafiltration and high performance liquid chromatography (HPLC). The classification study showed that these 4 peptides were of the true inhibitor type. The amino acid sequences of these peptides are YQDPRLGPTGELD-PATQPIVAVHNPVIV, PKDLREN, LLLAHLL, and NHRNRMMDHVH, respectively. Their individual IC50 (50% inhibitory concentration) values were as follows: 14.53 +/- 0.21 mu M, 9.82 +/- 0.37 mu M, 5.19 +/- 0.18 mu M, and 13.42 +/- 0.17 mu M. From sequence analysis, we determined that P-I was part of beta-casein in mare's milk. The 3 peptides P-K, P-M, and P-P did not correspond with any known milk protein. The results suggest that koumiss is rich in ACE inhibitory peptides, and the ACE inhibitors in koumiss are of the pro-drug type or a mixture of the pro-drug type and the true inhibitor type. These results may provide evidence about the beneficial effects of koumiss, especially on cardiovascular health.